This invention relates to the field of tooling spacer blocks or mandrels enabling fabrication of complex structures from individual component elements using diffusion bonding and similar element integrating techniques.
In the fabrication of sandwich-type structures, elements of layered cross-section, and devices of wedge shaped cross-section in one or more coordinate planes, it is often desirable to employ diffusion bonding element joining or integrating techniques. Diffusion bonded structures have found particular acceptance in the fabrication of state-of-the-art airframes, particularly when such airframes employ titanium as a fabrication material. The wing pivot bearing bosses and other highly stressed wing elements in the B-1 military aircraft, for example, have been found particularly amenable to fabrication from titanium and titanium alloy metals. The desirable strength-to-weight ratio and high corrosion resistance provided by titanium and titanium alloys is found to be particularly desirable in fabricating such aircraft structural assemblies.
Diffusion bonding as employed in the fabrication of these structural assemblies involves the application of heat and mutual force to the component elements being bonded with the heat and force environment continuing through periods of 10 hours or more in many instances. Since diffusion bonded structures can have overall dimensions measured in feet or tens of feet, the equipment used in performing diffusion bond operations is frequently massive in nature and requiring of considerable operating energy and generated forces.
Diffusion bonding equipment usually includes an assortment of spacing blocks or tooling fixtures used for both maintaining the elements of a to-be-bonded structure in correct relative position and for limiting deformation of the elements while in a pressured, elevated temperature environment, and a plastic flow state. Heretofore this tooling has been of a solid or homogeneous nature.
The weight and handling problems associated with homogeneous or solid tooling of such size can be appreciated to add considerably to the effort involved in fabricating a diffusion bonded structure. A homogeneous solid tooling block three feet long by four inches thick by three inches wide could be expected to weigh in the order of 120 lbs. for example, and to additionally require mechanical placement equipment and careful handling in order that neither the elements being bonded nor the tooling spacer blocks be damaged during placement. Nick and ding damage to such blocks, for example, would be transferred to subsequent diffusion bonded workpieces during a diffusion bond plastic flow interval.
The patent art includes several examples of diffusion bonding and other arrangements for joining materials using heat and pressure to achieve an atomic bonding between elements of the joined structure. In particular, the patent of G. L. Hitz, U.S. Pat. No. 2,998,646, discloses an apparatus and method for achieving high temperature and high pressure welding of two metal tube elements. The patent of W. V. Wenger, U.S. Pat. No. 3,114,202, illustrates a method for welding a hollow aluminum article using heat and pressure rollers. The patent of J. Melill et al., U.S. Pat. No. 3,533,153, illustrates a method for achieving diffusion bonds in a sandwich structure through the use of spacer bars or mandrels and also uses these tools in a stainless steel fabricated structure.
The patent of N. Klimmek et al., U.S. Pat. No. 3,533,156, shows use of tapered, solid or homogeneous mandrels for achieving a diffusion bonded structure. The Klimmek patent also indicates the feasibility of diffusion bonding with a variety of metals including aluminum, stainless steel, titanium, nickel, tantalum, molybdenum, zirconium, and columbium and their alloys. The Klimmek et al. patent also recites a list of prior patents involving solid state or intermolecular diffusion bonding.
The patent of D. E. Houston et al., U.S. Pat. No. 4,204,628, provides an additional example of the diffusion bonding of metal parts, especially parts made from copper.
The above-identified patent references indicate the use of diffusion bonding to be advantageous in the fabrication of strong, lighweight structures and also indicates the continued use of solid homogeneous tooling in the practice of diffusion bonding. The advantages of the present alternate to this solid homogeneous tooling will become apparent in the following description.